Bioavailability Parameters

This parameter represents the length of time required to attain the maximum concentration of drug in the systemic circulation. The parameter reflects the onset of action and, hence, can be utilized as a measure of the rate of absorption. The faster the rate of absorption, the smaller the value for the peak time and the quicker the onset of action of the drug. The peak time is determined by using the following equation  

1 clearly indicates that larger the value of the absorption rate constant ( a), the smaller is the value of peak time ( max) and the quicker is likely to be the onset of action. 

Area under the Plasma Concentration Time Curve 

All the terms of the Eq. 2.4 have been defined previously. Eq. 2.4 can further be reduced to 

There are a number of factors responsible for the variation in bioavailability. Broadly speaking, these factors can be classified as patient related or dosage form related. Patient related factors include age, disease state, abnormal genetic characteristics, and gastrointestinal physiology. The detailed discussion on these factors is beyond the scope of the objectives of this chapter. 

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Table 2 Bioavailability Parameters Obtained in Male Beagle Dogs (mean SD, n = 3) After Oral Administration of 50 mg of Hf Base Formulated as Either a Long chain Self-microemulsifying Formulation (SMEDDS) or a Medium-chain Self-emulsifying (SEDDS), or Self-microemulsifying Drug Delivery System (SMEDDS)...

Bioavailability Parameters and Their Influence on Rate and Extent of Absorption... 

The ratio comparative (relative) bioavailability is assessed by comparing the bioavailability parameters derived from plasma drug... 

Compare bioavailability parameters for products being tested (AUC)o, peak plasma concentration, peak time and/or amount of drug excreted in urine... 

Tables 7.5 and 7.6 show bioavailability parameter values and pharmacokinetic parameter values for theophylline following the oral administration...

Table 7.5 Bioavailability parameters for theophylline after oral administration of 300 mg dose through liquid or capsule dosage forms to 14 subjects ...

The CyD complexes of HCFU were expected to have good bioavailability after oral administration, because the dissolution and chemical stability of the complexes were superior to those of HCFU alone. Consequently, HCFU and its three CyD complexes were administered orally to rabbits to evaluate their absorption characteristics. The mean serum levels of 5-FU following the oral administration of HCFU of its CyD complex are shown in Figure 5. The bioavailability parameters were calculated from the serum level-time curves up to 8 hours post administration, and the results are summarized in Table I. 

TABLE I. Bioavailability parameters of HCFU and its CyD complexes following the oral administration (equivalent to 15 mg/kg HCFU) to rabbits... 

TABLE III. Bioavailability parameters of CPZ following the intramuscular injection in the absence and presence of 3-CyD... 

The bioavailability parameters in the combination of the complex with DL-Phenylalanine, C and AUC, increased with the dose of DL-phenylalanine. There was observed no change in T in the simultaneous administration with DL-phenylalanine, though the reason is not clear because a bioavailability phenomenon is a quite complicated one. 

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